|"I bought replacement cartridges for the CP1518 LaserJet. Ended up having to replace all three color cartridges."|
It has 3 cartridges, not 4 (one black) ?
"How can they all run out of toner at the same time?"
It depends on what you're been printing. If you print a lot of black, you have only 3 cartridges, they will probably have similar amounts of toner left.They may be more or less all out of toner at about the same time, they may not be.
What I would have done when the software is telling you all three need to be replaced is....
- use something to weigh each of the original ones, compare than to the new one.If the cartridges are identical that will give you an idea whether the other two have more toner in them.
- if the weights indicate there is still significant toner in the other two, un-install the HP software for the printer, install it again.
"Am I right to think there is a time limit that drives replacement?"
I have never heard of that for toner cartridges.
If they DO have a chip that keeps track of the total time the cartridges have been used,or the number of times they have been used, or similar, there would be visible electrical contacts (more than two) on the outside of the cartridges somewhere that connect to contacts in the printer when you install them, and in that case there are probably cheap chip re-setters available on the web.
If the total time the cartridges have been used is kept track of on the hard drive in the printer's software, which I doubt, un-installing the HP software and re-installing it should get rid of that info after the chips have been re-set.